Gas exchange valves are used in internal combustion engines to control fluid connections between the cylinder and a supply of intake air or intake air and other gases such as recirculated exhaust gas, or between the cylinder and an exhaust manifold for expelling combustion products during operation. Designs are known wherein a single intake valve and a single exhaust valve are associated with each cylinder in an engine, as well as designs where multiple gas exchange valves of each respective type are associated with each cylinder. A camshaft, typically rotated at half engine speed, is coupled with valve lifters, bridges, rocker arms, and/or other equipment for controlling the opening and closing of gas exchange valves at appropriate engine timings.
Gas exchange valves are moved out of contact with and into contact with the engine head or a valve seat insert within the engine head to effect their opening and closing actions. Gas exchange valves may be moved between their open and closed positions with significant mechanical forces, and are exposed to combustion temperatures of several hundred degrees along with relatively high in-cylinder pressures. These and other factors contribute to the gas exchange valve environment being quite harsh. It has been observed that gas exchange valves and valve seats or valve seat inserts can exhibit a phenomenon over time known as valve recession. Over the course of an engine's service life, or between service intervals, the contacts between a gas exchange valve and its valve seat can number in the millions or potentially even billions. The harsh conditions and great number of impacts can cause material of which the gas exchange valve and/or the valve seat is formed to wear away and/or become deformed, so that the valve “recedes” toward or into the engine head further than what is desired. Where valve seat recession becomes severe enough engine operation or performance can be compromised, sometimes requiring a so-called top end overhaul prematurely. Engineers have experimented with a variety of different techniques attempting to ameliorate the extent and effects of valve seat recession and other valve wear patterns. One strategy apparently aimed at preventing the outer diameter side of a valve face from locally wearing is set forth in Japanese Patent Application Publication No. JP8270417A. According to the '417 reference, a convex surface bulging toward a seat surface of a valve face abuts against the seat surface of a valve seat to address local wear problems.